JP2001227851A - Cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling device for cooling either a specimen or a sensor down to such a boiling temperature of helium in which both time and work for performing a cooling operation can be saved without requiring any cooling in the device carried out in advance under application of liquid nitrogen. SOLUTION: This cooling device has a structure in which a liquid helium storing tank is not installed in a vacuum chamber, but in place of it, a port for feeding liquid helium is installed in view of thermal insulation, a liquid helium container and the port are connected by a vacuum thermal insulating pipe and liquid helium is supplied directly from the container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample made of various devices and materials, such as various semiconductor devices and semiconductor materials, or superconducting materials, other metal materials and inorganic materials, at a low temperature up to the boiling point of a liquefied gas. The present invention relates to a device for cooling and maintaining a low temperature when performing measurement, observation, or operation.

[0002]

2. Description of the Related Art Recently, a high-sensitivity magnetometer having a spatial resolution of about a micrometer called a SQUID (superconducting quantum interferometer) microscope has been put into practical use, and various elements and materials have been measured using a SQUID microscope. To do more and more. Since SQUID uses superconductivity, it needs to be cooled to a low temperature of liquid nitrogen temperature or lower (several K to 77K), and the other party's sample often needs to be kept at a low temperature. In addition, when observing a sample with a tunnel microscope or an atomic force microscope in addition to the SQUID, the sample may be kept at a low temperature. FIG. 2 is a schematic view showing an example of a conventional cooling device for cooling a sensor side to a low temperature. Inside the vacuum chamber 10, a triaxial scanning stage 20, a cooling head 30, a storage tank 40, a sensor 50, a sample 60, and the like are installed. Outside the vacuum chamber 10, a vacuum pump 70, a liquid helium container 80, A vacuum insulation pipe 90 is provided.

The vacuum chamber 10 is made of stainless steel, and the inside thereof is kept at a vacuum in order to insulate the outside from the outside.

[0006] The triaxial scanning stage 20 is used for setting a sample 60 and controlling a relative position between the sensor 50 and the sample 60.

[0005] The cooling head 30 is made of oxygen-free copper and holds the sensor 50 in thermal contact.

[0006] The storage tank 40 holds a refrigerant for cooling the cooling head 30. Since liquid helium is used as the refrigerant, in order to store liquid helium in the storage tank 40, the liquid helium is connected to the liquid helium container 80 using the vacuum insulated pipe 90 and transferred. In order to reduce heat intrusion, a refrigerant tank 4 for heat insulation is provided around the storage tank 40.
1 is installed to hold liquid nitrogen.

As the sensor 50, an SQUID having a detection coil having a diameter of about 10 μm was used. Niobium operating at about the boiling point of liquid helium was used as the superconducting material for producing the SQUID.

By operating the vacuum pump 70, the refrigerant stored in the storage tank 40 is transported to the cooling head 30 through the pipe 31, cools the cooling head 30, and is discharged from the pipe 32 through the vacuum pump 70 to the outside. Is done.

In the procedure for measuring the magnetic field distribution of the sample 60, first, liquid nitrogen is stored in the storage tank 40 and the insulating refrigerant tank 41, and the periphery of the storage tank 40 is cooled down to the boiling point of liquid nitrogen. Next, the liquid nitrogen contained in the storage tank 40 is removed, and the storage tank 40 and the liquid helium container 8 are removed.
0 is connected to the storage tank 40 by connecting the liquid helium as a refrigerant to the storage tank 40. Thereafter, the liquid helium is passed through the cooling head 30 by operating the vacuum pump 70, and the cooling head 30 is cooled to about the boiling point of helium.
The relative position between the sensor 50 and the sample 60 is controlled using 0, and measurement is performed by recording a signal from the sensor 50.

[0010]

In the above-mentioned conventional cooling device which needs to cool the sensor or the sample to a low temperature,
Since it is necessary to transfer and hold liquid helium to the storage tank provided in the vacuum chamber, before the transfer, once the liquefied gas such as liquid nitrogen is put into the storage tank and the storage tank is cooled to the boiling point of the liquefied gas in advance. It is necessary to remove the liquefied gas immediately before the transfer of the liquid helium, and furthermore, it is necessary to fill the liquefied gas such as liquid nitrogen into the heat-insulating refrigerant tank 41 installed around the storage tank. It takes time and effort to cool to a low temperature, and there is a problem that a refrigerant such as liquid nitrogen needs to be prepared. Furthermore, since it is necessary to hold liquid helium once in the storage tank, the amount of liquid helium consumed for cooling the storage tank is reduced by the cooling head, especially when the time to cool the sensor or sample to low temperature is short. There is a problem that the amount of liquid helium is not negligible compared to the amount of liquid helium consumed for cooling the liquid, and as a result, the loss of liquid helium is large. Furthermore, since the storage tank for liquid helium is provided in the vacuum chamber, there is a problem that the vacuum chamber becomes large and the installation area of the cooling device becomes large.

[0011]

Means for Solving the Problems (First Means) In order to solve the above-mentioned problems, the present invention does not provide a liquid helium storage tank in a vacuum chamber, but instead uses a liquid in consideration of heat insulation. Install a port for helium introduction,
The liquid helium container and the port are connected by a vacuum insulated pipe, and the liquid helium of the refrigerant is directly supplied from the container. (Second Means) In addition to the first means, the vacuum insulation pipe is a double vacuum pipe. (Third Means) In addition to the first means, a heat shield plate is provided around the port. (Fourth Means) The third means further has a structure in which helium exhausted from the cooling head is passed through the inside of the heat shield plate. (Fifth Means) In addition to the third means, a port for introducing liquid helium is constituted by a plurality of materials.

According to the structure of the cooling device according to the first means, there is no need to transfer and hold the liquid helium to the storage tank having a large heat capacity, and the helium is supplied from the liquid helium container directly to the cooling head through the heat insulating pipe. In addition, since it is not necessary to previously cool the inside of the vacuum chamber using a refrigerant such as liquid nitrogen, it is possible to save time and labor.

According to the second means, the amount of heat entering the vacuum heat insulating pipe between the vacuum chamber and the container can be reduced as much as possible, so that the consumption of liquid helium can be suppressed.

According to the third means, a heat insulating refrigerant tank around the port is not required, so that it is not necessary to prepare a refrigerant such as liquid nitrogen for heat insulation, and the installation area can be reduced because the vacuum chamber can be downsized. Can be reduced.

According to the fourth means, since the ability to cool the heat shield plate is improved, heat intrusion into the port and the first pipe is reduced, and liquid helium can be used effectively.

According to the fifth means, the ability to cool the heat shield plate is improved, and the amount of heat entering the port from outside can be reduced, so that the heat intrusion into the port and the first pipe is reduced. And liquid helium can be used effectively.

The sensor in the present invention is SQ
Observe the surface shape and state of the sample, such as probes for tunnel microscopes and atomic force microscopes, as well as sensors for measuring the magnetic flux and various radiations generated from the sample, such as the SQUID in a UID microscope, and the physical properties and characteristics of the sample. It also includes a probe to be used.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic diagram showing the structure of a cooling device according to Embodiment 1 of the present invention.

A three-axis scanning stage 20, a cooling head 30, a port 42 for introducing liquid helium, a sensor 50, a sample 60, and the like are installed in the vacuum chamber 10. A vacuum pump 70, A liquid helium container 80 and a vacuum insulation pipe 90 are provided.

The vacuum chamber 10 is made of stainless steel, and is kept in a vacuum for thermal insulation with the outside.

The three-axis scanning stage 20 is used for setting the sample 60 and controlling the relative position between the sensor 50 and the sample 60.

The cooling head 30 is made of oxygen-free copper to improve heat conduction, and holds the sensor 50 in a state of being in thermal contact.

The port 42 is for introducing liquid helium to the cooling head 30 installed in the vacuum chamber. The liquid helium stored in the liquid helium container 80 is introduced into the cooling head 30 by connecting the port 42 and the liquid helium container 80 with a vacuum insulation pipe 90. In order to reduce heat intrusion around the port 42, a heat insulating refrigerant tank 41 having a shape surrounding the port 42 is installed to hold liquid nitrogen.

As the sensor 50, an SQUID having a detection coil having a diameter of about 10 μm was used. As a superconducting material for producing the SQUID, niobium operating at about the boiling point of liquid helium was used.

The vacuum pump 70 is used to reduce the pressure inside the second pipe 32, the cooling head 30, the first pipe 31, and the vacuum insulation pipe 90, and to transfer the liquid helium in the liquid helium container 80.

The procedure for measuring the magnetic field distribution of the sample 60 is as follows.
Is cooled to the boiling point of liquid nitrogen. Next, the port 42 and the liquid helium container 80 are connected to the vacuum insulation pipe 90.
By operating the vacuum pump 70, the liquid helium in the liquid helium container 80 is passed through the cooling head 30 to cool the cooling head 30 to about the boiling point of helium. After cooling the cooling head 30, the sensor 50 is operated, and the sensor 50 is
The measurement is performed by controlling the relative position between the sample and the sample 60 and recording the signal from the sensor 50. (Embodiment 2) FIG. 3 is a schematic diagram showing the structure of a cooling device according to Embodiment 2 of the present invention. Vacuum insulation pipe 90
There is no difference between the first embodiment and the first embodiment except that a double vacuum pipe is used.

FIG. 4A is a diagram showing a cross-sectional structure of a vacuum heat insulating pipe 90 according to the second embodiment of the present invention.
(B) is a diagram showing the structure of the port 42 and the tip of the vacuum insulation pipe 90. The central pipe of the double vacuum pipe is a path for passing helium transported to the cooling head, and the outer peripheral pipe is a path for passing helium exhausted from the cooling head.

By operating the vacuum pump 90 connected to the outer peripheral pipe of the vacuum heat insulating pipe 90, the outer peripheral pipe of the vacuum heat insulating pipe 90, the second pipe 32, the cooling head 30, the first pipe 31, and the vacuum heat insulating pipe The pressure of the central pipe 90 decreases, and the liquid helium in the liquid helium container 80 is transferred. The helium path is transferred from the liquid helium container 80 to the cooling head 30 through the central pipe of the vacuum insulation pipe 90 and the first pipe 31, and after cooling the cooling head 30, the vacuum insulation is performed from the second pipe 32. Piping 9
The gas is evacuated from the vacuum pump 90 through the outer peripheral pipe 0. (Embodiment 3) FIG. 5 is a schematic diagram showing a structure of a cooling device according to Embodiment 3 of the present invention. The configuration other than the configuration in which the heat shield plate 44 is provided in place of the elimination of the heat insulating refrigerant tank 41 is the same as that of the second embodiment.

FIG. 6 shows the structure around the heat shield plate 44. The heat shielding plate 44 is formed by processing a single plate into a cylindrical shape, and is thermally connected to the outer wall of the port 42 which is cooled to a temperature not higher than the boiling point of liquid nitrogen. When the port 42 is covered with the heat shielding plate 44, a hole is made in a part of the side surface, and the first and second pipes 31 and 32 are passed. The heat shield plate 44 was made of oxygen-free copper to improve heat conduction. (Embodiment 4) FIG. 7 is a schematic diagram showing a peripheral structure of a heat shield plate 44 of a cooling device according to Embodiment 4 of the present invention. The configuration other than the structure of the heat shield plate 44 and the method of connecting the second pipe 32 and the port 42 are the same as those of the third embodiment.

The heat shield plate 44 is a double-structured cylinder having a sealed space inside as shown by a broken line in FIG.
And port 42. Helium after cooling the cooling head 30 is passed through the space inside the heat shielding plate 44. Although the internal space is hollow, a net or particles of oxygen-free copper may be inserted as a cold storage material. The heat shield plate 44 was made of oxygen-free copper to improve heat conduction. (Embodiment 5) FIG. 8 is a schematic diagram showing the periphery of a port 42 in a cooling device according to Embodiment 5 of the present invention. Other than the material of the port 42, there is no difference from the third embodiment. Vacuum chamber 1 at port 42
The portion A which is in direct contact with the outer wall 0 is made of a material having a low thermal conductivity, and the portion B is made of a material having a high thermal conductivity. Specifically, G-FRP was used as a material having a low thermal conductivity, and oxygen-free copper was used as a material having a high thermal conductivity.

[0032]

According to the present invention, it is not necessary to install a liquid helium storage tank in a vacuum chamber. Therefore, it is necessary to cool the storage tank in advance using a liquefied gas such as liquid nitrogen before transferring helium. Since there is no need to perform the operation of extracting the liquefied gas, the labor and time required for cooling the sensor or the sample to a low temperature can be saved.

Further, since the heat-insulating refrigerant tank 41 installed around the storage tank is not required, labor for filling the refrigerant can be saved, and it is not necessary to prepare a refrigerant such as liquid nitrogen.

Furthermore, even when the time for cooling the sensor or the sample to a low temperature is short, helium is transported to the cooling head only when cooling is necessary, so that loss of liquid helium can be suppressed.

Further, since no liquid helium storage tank is provided in the vacuum chamber, the vacuum chamber can be reduced in size, and the installation area of the cooling device can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a structure of a cooling device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a structure of a conventional cooling device.

FIG. 3 is a schematic diagram illustrating a structure of a cooling device according to a second embodiment of the present invention.

FIG. 4A is a diagram showing a cross-sectional structure of a vacuum heat insulating pipe 90 according to Embodiment 2 of the present invention. (B) is a diagram showing the structure of the port 42 and the distal end of the vacuum insulation pipe 90 according to Embodiment 2 of the present invention.

FIG. 5 is a schematic diagram illustrating a structure of a cooling device according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a structure around a heat shielding plate 44 according to Embodiment 3 of the present invention.

FIG. 7 is a schematic diagram showing a structure around a heat shield plate 44 of a cooling device according to a fourth embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating a periphery of a port in a cooling device according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vacuum chamber 20 3-axis scanning stage 30 Cooling head 31 First piping 32 Second piping 40 Storage tank 41 Insulating refrigerant tank 42 Port 44 Heat shielding plate 50 Sensor 60 Sample 70 Vacuum pump 80 Liquid helium container 90 Vacuum insulated piping

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Atsushi Nagata 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba F-term (reference) in Seiko Instruments Inc.

Claims (5)

[Claims] A cooling head for cooling the liquefied gas to about the boiling point, a storage tank for storing liquid helium for cooling the cooling head, and helium transported from the storage tank to the cooling head. A pump for exhausting, a first pipe connecting the storage tank and the cooling head, a second pipe connecting the cooling head and the pump, the cooling head, the storage tank, and the first pipe. A vacuum chamber that insulates at least a portion of the second pipe from the outside air, a liquid helium container for filling and transporting liquid helium, and a vacuum insulation for transporting liquid helium from the liquid helium container to the storage tank. In a cooling device composed of a pipe and
A cooling device, wherein the storage tank is not provided in the vacuum chamber, and a port for introducing liquid helium into the vacuum chamber is provided instead. 2. The cooling device according to claim 1, wherein said vacuum insulation pipe is a coaxial double vacuum pipe. 3. The cooling device according to claim 1, wherein the heat insulating refrigerant tank is not provided, and a heat shield plate is provided around the port instead. 4. The heat shield plate is a sealed container, and helium from the second pipe is introduced into the heat shield plate.
4. The cooling device according to claim 3, wherein the port is evacuated. 5. The cooling device according to claim 3, wherein said port is made of a plurality of materials having different thermal conductivities.